The present invention generally relates to more electric aircraft and, more particularly, to electric power distribution systems and condition based maintenance for aircraft.
There has been a growing trend in developing more electric aircraft (MEA). The MEA concept employs an overall system approach to optimizing the airframe and engine systems of aircraft on the premise that significant benefits can be achieved by replacing today's pneumatic, hydraulic and electric airframe power systems with predominantly electric power. The trend toward MEA creates increased demands for electric power and more sophisticated power distribution and load management systems. As a result, more and more intelligence has been incorporated into such aircraft electric power distribution and load management systems, leading to opportunities for the integration of such systems with other aircraft functions. For example, integrated modular avionics (IMA) and aircraft system health monitoring functions may be integrated with a power distribution system due to the fact that the power distribution system has access to a significant portion of aircraft equipment.
The trend toward more electric aircraft, at the same time, accelerates the incorporation into aircraft of electrical components that are flight-critical—such as actuators, and fuel and hydraulic system pumps and valves. Aircraft operators, in the mean time, driven by safety and cost concerns, have gradually shifted their focus in maintaining electric equipment from the traditional time based maintenance (TBM)—a reactive approach based on tracking the in-service time of each component—toward a more proactive condition based maintenance (CBM) based on sensing the actual condition of each component. CBM may be applicable, for example, to electrical actuators, electrical fuel system components (pumps and valves), arc fault protection, wiring, power generation components, avionics, and fan motors.
For example, the introduction of high voltage DC systems accentuates the problem of arcing of electrically powered systems, which is a major safety concern for aircraft. Arcing may be categorized as series, parallel, or wet arcing. Series arcs are typically caused by vibration that causes intermittent arcing due to a poor or loose connection within a circuit. Such series arcs typically create a lot of heat in a short space of time. They are difficult to locate at an early stage during ground maintenance and are a major fire hazard. Parallel arcs are shorts between adjacent wires or of a wire to a structure. They are typically caused by insulation breakdown (e.g., chafing) or abrasion of a wire bundle. Parallel arcs are also a major fire hazard. Wet arcs are the shorting between two adjacent damaged cables by an electrolyte. Typically, aircraft are susceptible to wet arcing in the undercarriage and wing fold areas where moisture, cleaning fluid, oil, and hydraulic fluid leaks are common. In commercial aircraft such conditions can occur under the toilets.
Methods to accurately predict impending failure of electrical loads and to predict and protect against arcing faults in aircraft wiring can form an important part of any condition based maintenance program. CBM may provide more reliable and cost effective maintenance through the extensive use of sensing signals, sophisticated software programming, and data processing to track the health of the system under consideration.
In an advanced aircraft secondary power distribution system (SEPDS), every electric load using secondary power may be controlled by a load management module (LMM) capable of sampling the instantaneous load current and voltage. These load current and voltage measurement signals can constitute the key characteristics of a majority of electric loads and their feeders (i.e., wirings), and can be used along with other necessary information to determine the health of the load and feeder systems.
As can be seen, there is a need for a more integrated aircraft secondary power distribution system which not only performs the traditional electric load management functions, including control and protection, but also integrates health monitoring functions and prognostic information for the loads and feeders that connect to the secondary power distribution system.